This invention relates to a walking beam furnace for heating workpieces while advanced through the furnace by walking beam assemblies having a body of refractory and a cooling system including pipes at opposite lateral sides of the body of refractory below the workpiece-engaging face thereof. More particularly, the present invention relates to an improved construction and relationship of parts to support and cool a body of refractory material without rupture or failure to the integrity of the cooling system.
It is well known in the art to reheat ingots, blooms, slabs, billets and similar workpieces in a walking beam type furnace for subsequent processing in a rolling mill. The workpieces are delivered in succession by a suitable conveyor system into the chamber of the furnace having burners arranged to heat each workpiece up to a desired temperature before it is discharged onto a furnace-delivery table. The workpieces are advanced in the furnace chamber with step-by-step movements by walking beam assemblies that form stationary and movable supports for the workpieces. The movable supports first lift the workpieces from the stationary supports and then advance by movement toward the exit end of the furnace through a predetermined distance. The movable supports are then lowered to deposit the workpieces on the stationary members for support thereby. The movable supports are then retracted while spaced below the bottom surface of the workpieces to a starting position for a succeeding cycle to lift and advance the workpieces. Usually, two or more lifting beam assemblies extend in the direction of the length of the furnace chamber along the lateral sides of the stationary support to collectively form the walking beam assemblies. Heat insulating material, such as refractory, is usually provided in the furnace on the various surfaces along the hearth that contact and support the workpieces during movement within the furnace chamber. Such material is used to at least minimize, if not eliminate, the development of cold spots in the workpieces at the points of contact with the supporting surface of the walking beam assemblies. The heat insulating material, usually comprised of hightemperature refractory, must include a support having coolant facilities to restrain movement and prevent overheating.
In the past, a water-cooled channel was used to retain the hearth refractory and support the load imposed on the refractory by the workpieces as shown, for example, in U.S. Pat. No. 3,450,394. The water-cooled channel is comprised of a carbon steel weldment consisting of a plate section welded along its side edges to the end flanges of a channel section. The hollow area thus formed in the channel with the end plate is coupled to water-supply and discharge pipes. The opposite ends of the weldment are closed by end plates that are welded in place. The water-cooled channel is arranged on the support for the refractory such that the elongated enclosed water channel is orientated vertically on the refractory support and embedded in the side edge of the refractory. An L-shaped clip, in cross section, made of alloy material has one leg section welded to the top edge of the water-cooled channel such that the free leg section of the clip extends vertically along the outer side edge of the refractory for support of the refractory as well as cooling by conductive heat transfer.
The water-cooled channel and support-clip arrangement have been plagued with problems. Water leaks occur at weld failures due to differential cooling to the weldment forming the coolant channel. The leakage of coolant water cannot be tolerated in a furnace of this type for heating workpieces. Moreover, the upstanding leg of the alloy clip that extends along the side edge of the refractory curls outwardly away from the refractory because of differential heating/cooling, thus rendering it useless for its intended use for support of the refractory. Moreover, welding of the alloy clip to the carbon steel forming the water-cooled channel is a difficult undertaking because of the need to weld widely different metals. It is absolutely essential that the workpieces undergo heating in the furnace without any contact with the water-cooled channel and the refractory support clip which are cooled by conductive heat transfer. It has been found that the thermal stresses which develop in the weldment are a predominant cause leading to weld failures that permit water to leak from the coolant channel. It has also been found that sharp edges and corners in the known cooling channel arrangement promote scale and dirt accumulations that adversely affect the operation of the walking beams. In particular, the outward curling of the clip provides an open cavity into which scale can accumulate and possibly even extend up along the refractory into heat conductive transfer with a workpiece which, of course, cannot be tolerated. The necessary support for the refractory is reduced or ineffective when its clip curls outwardly.